How to choose a mosfet to control 3 light bulbs of 4,5V 0,8A from Arduino

Hi,

I need to control (power/on and dimm) 3 light bulbs of 4.5V and 0.8A from an Arduino nano.

If I'm not mistaken a 5V output of an Arduino nano can provide up to 0.8A so to power 3 of them I think I'm going to need to power them from an external power supply and control them using Mosfets.

But I'm completely lost with the mosfets, I don't know which one to choose.

Could someone point me in the right direction?

thanks!

An Arduino cannot safely supply 800mA.

Use a logic level MOSFET.

Pick a low RDSon value for a gate voltage input of 5 volts. (assume 5v Arduino).
Vgs maximum must be greater than VDD.

cct. C1 should work, see reference numbers at the bottom of the schematic.
Change 12v to 5v.

Lights replace M3 and D3.

You don't necessarily need a separate power supply, and a 4.5V supply is probably going to be hard to find. The bulbs will probably work from 5V (I assume they are regular incandescent bulbs?) or you can put a diode in series to drop around 0.6V.

If you use "one big" 5V power supply, the MOSFETs/lights should have a separate connection to the power supply (the current shouldn't go through the Arduino board).

[u]Here is a MOSFET driver circuit[/u]. You can leave-out D1 since you have a non-inductive load (but as above you can optionally add a series diode).

The two main considerations are current rating (plus, allow some safety margin) and as Larry says, get "logic level" MOSFET because a regular MOSFET needs more than 5V to control it.

And, you may need a heatsink. (It can be tricky to predict but if the MOSFET gets too hot to touch, or if it burns-out, you need a heatsink. ;) )

For both the power supply and the MOSFET, the current should meet or exceed the actual current requirements. i.e. It's OK to use a power supply and/or MOSFET rated for 10 Amps.

The MOSFET voltage rating won't be an issue because any MOSFET can handle 5V.

It would help to know things like:

  • How far will these light bulbs be from the Arduino?
  • Will they be next to each other, or widely spaced from each other, or...?
  • Or, asking from a different tack: does it make more sense to power all three lamps from on MOSFET, or would one MOSFET per lamp be the way to go?
  • I'm assuming that 800mA specification is the sum of currents from all three lamps. Correct me if I'm wrong.
  • Any chance they can be run in series? Like from a 4.5 * 3 = 13.5V power source [or even a 12V power source]?
  • Can they be "ground switched"? Or must they be switched from the "High-Side"? I.e. the MOSFET on the ground side of the lamp, vs the positive power side?
  • These are filament bulbs, correct?
  • And, knowing the actual application would, probably, avoid the need for such lists of questions ;)

Thank you very much for your replies! I'm going to need some time to digest all that info (first time using mosfets) and I'm still ultra confused about the numbers and parameters. :)

I'm going to read an intro, go back to your replies and try to process it. :)

I'll be back :)

thank you for your questions! here we go:

How far will these light bulbs be from the Arduino?
About 15cm

Will they be next to each other, or widely spaced from each other, or…?
Widely spaced

Or, asking from a different tack: does it make more sense to power all three lamps from on MOSFET, or would one MOSFET per lamp be the way to go?
I need to power them on and dimm them separately. I think I’m going to need one mosfet per lamp.

I’m assuming that 800mA specification is the sum of currents from all three lamps. Correct me if I’m wrong.

Well, it’s an filamente bulb and in the box says 4,5V 0,8A. I asume that what it will take when fully bright.

Any chance they can be run in series? Like from a 4.5 * 3 = 13.5V power source [or even a 12V power source]?
Not sure…because I’m innexperienced with this. But since I need to operate them separately I think they cannot be in series…but…not sure. What do you think?

Can they be “ground switched”? Or must they be switched from the “High-Side”? I.e. the MOSFET on the ground side of the lamp, vs the positive power side?
These are filament bulbs, correct?

Yes they are filament bulbs. Not sure to understand the difference between ground and high-side switched. If I can turn them on/off and dimm them from the arduino I don’t have any preference :slight_smile: But again, newbie here and not sure.

And, knowing the actual application would, probably, avoid the need for such lists of questions :wink:

That’s the fun part. I’m attaching an image of an early prototipe the contraption I need to wire. Whe the star button is pressed, the lights will start a cycle of on/off/dimming like a game and one of them will be finally on revealing (using a servo) whats behind the cup.

Vgs maximum, and RDSon are found in the MOSFET data sheet.

An IRL3705N should do nicely.

https://www.infineon.com/dgdl/irl3705n.pdf?fileId=5546d462533600a40153565f29f42532

OP’s image.

Lights can be placed in series, but recommend you use them in parallel.

A 4.5v bulb will work at 5 volts, however if you are concerned, add an appropriate series dropping resistor (to drop .5v) with each bulb.

As mentioned, circuit C1 (GND side switching) will work.

larryd:
Lights can be placed in series, but recommend you use them in parallel.

NOT! The OP stated that each lamp needs to be controlled separately. So, 1 MOSFET per lamp [i.e. separate circuits, so neither *series*, nor *parallel*].

larryd:
A 4.5v bulb will work at 5 volts, however if you are concerned, add an appropriate series dropping resistor (to drop .5v) with each bulb.

Or, as DVDdoug suggested, a series diode, such as a 1N4004.

larryd:
As mentioned, circuit C1 (GND side switching) will work.

Like this:


Notes:

  • I show an "Uno" here, but this applies just a well to a Nano.
  • V2+ in this case is 5V. The Nano's 5V pin won't be able to supply the current needed [unless you take my advice, and run those lamps at a very low current [see below] -- then the 5V pin might do it just fine.
  • The lamps are connected across +Out and -Out. One lamp per +Out/-Out pair. No need to worry about polarity -- you can connect the lamps either way.
  • Diodes D2, D3 and D4 are optional, and merely to drop 5V down to more like 4.3V. Replace each diode with a wire, if not used. But, consider that if you want these bulbs to last longer, better to drive them below their specified power. Adding the diode will work towards this. Also, for that "Steampunky" look, you probably want the bulbs to glow more of an orange -- you know, where you can actually look directly at the filaments -- where they look like orange glowing filaments--right? In which case, instead of the diodes, resistors might to a better job, as the voltage across the lamps may need to come down even lower than 4.3V[ish]. And, even if you plan to use PWM to dim these bulbs, it still might be worthwhile to add the diode, or resistor, especially if you adopt the other goal of getting the maximum current down, so the Nano's 5V regulator can supply those bulbs [and, remember, it's the TOTAL current -- unless it will never be the case that more than one lamp will be on at once [and if that is a shell-game contraption, then I guess that WOULD be the case]. Figure on a practical upper limit of 500mA from the Nano. ALSO [yet again]: You can, probably eliminate the Diode/Resistor by merely relying on PWM do ALL the dimming -- i.e. the maximum brightness would always be something less that a Duty Cycle [something else for you to look up :wink: ]of 100%.
  • My selection of Arduino outputs D2, D5 & D8 was arbitrary -- and merely to make the schematic easier to draw :wink:
  • For education purposes: The MOSFETs are in a "Low Side Switching" arrangement. Because, they switch the low side of the device [lamp] being controlled/"switched".

ReverseEMF: NOT! The OP stated that each lamp needs to be controlled separately. So, 1 MOSFET per lamp [i.e. separate circuits, so neither series, nor parallel].

Yes, missed that.

Or, as DVDdoug suggested, a series diode, such as a 1N4004. That would be better.

Here's one for my Forum Buddies regarding using PWM to control the brightness of a Filament lamp and the longevity of said lamp:

In terms of longevity, will PWM cause flexing of the filament, due to temperature variations, and will that fatigue the filament -- causing it to fail sooner? I would think the PWM frequency would figure into that.

And, if the answer is Yes, then perhaps something like an RC low-pass filter feeding the Gate, such that the MOSFET runs as a Class-A amplifier?

? ? ? ? ? ? ?

“In terms of longevity, will PWM cause flexing of the filament, due to temperature variations, and will that fatigue the filament -- causing it to fail sooner? I would think the PWM frequency would figure into that.”

Interesting question.

Since the PWM frequency is high, the filament temperature will probably be quite constant.

I have a set of old HP logic probes that use 4.5v volt bulbs for indicators.

Haven’t had to replace them, with a ‘pulse train’ intensity varies.

In the old days similar lights were used as alarm flashing indicators (on/off) they worked well but the filaments did have internal support.

ReverseEMF:
In terms of longevity, will PWM cause flexing of the filament, due to temperature variations, and will that fatigue the filament – causing it to fail sooner? I would think the PWM frequency would figure into that.

No, nothing bad happens, the thermal mass of the filament is too high(*) to respond to PWM. Running the bulb
at lower currents will definitely increase its life by reducing evaporation from the filament (unless its a tungsten halogen bulb which must always be operated at full temperature). So PWM dimming will increase the life, not reduce it.

By the way metals don’t fatigue without significant stress placed on them, a filament’s own weight isn’t a significant stress.

(*) except perhaps for very low current filaments.

And, another [crazy?] thought:

Rather than an extra resistor, to drop the voltage, to the Lamp, from 5V to around 4.5V, how about a MOSFET with a high channel resistance – BOOM! Two birds with one stone!

0.5V / 800mA = 625mΩ

Such as the IRFD110
At around 800mA, this guy should have around a half volt drop across it’s channel, with 5V on it’s Gate. As the MOSFET gets hot, the channel voltage will rise, causing the Lamp to dim, and it’s resistance to go up. Thus, the Drain current should reduce, and the thing should find an equilibrium point. Or do I have that wrong?

And, it looks like the IRFD110 MOSFET can survive this madness, too.

Wow, you guys are incredible. Thank you very much for all this educational material and schematics. I really, really, appreciate it.

I’ll try to get all this material at my local shop and run some tests.

I was so comfy in my just-arduino world with motors and code that now -descending into the pure the electronics- my brain hurts….

(apologies for any mistakes, english as second language)

Again, in the old days we would place a resistor from the drain (collector for BJTs) to GND.

This resistor was picked so the filament was just under that of glowing.

The life of the lamps increased considerably.

ReverseEMF: - For education purposes: The MOSFETs are in a "Low Side Switching" arrangement.

[/quote]

For Q6, Q7 and Q8 (that I understand are the mosfets) and given all the resistors that you layed out, do you have a specific MOSFET in mind?

For Vdd = 5v IRL3705N, IRL540 or IRLZ44N will work.

Well, I beggining to grasp it a little bit and learning a lot of new concepts.

ReverseEMF, in you schematic, what is the purpose of the resistors R12 and R11 placed before the mosfet’s gate?

“in you schematic, what is the purpose of the resistors R12 and R11 placed before the mosfet's gate?”

R12 keeps the MOSFET ‘OFF’ at Arduino power up time. The Arduino pin ‘floats’ at this time and this resistor keeps the gate discharged.

R11 limits the ARDUINO output current to a safe level.